Candida albicans is a pathogenic yeast which resides as a commensal in the oral cavity of a majority of healthy individuals. However, under a number of predisposing conditions, C. albicans invades tissue causing infection. It has been assumed that commensal strains are the source of subsequent infection and that there is little strain specialization. However, these assumptions have recently been questioned by results which demonstrate that different strains are carried in different anatomical locations of the same healthy women, that strain replacement occurs in the oral cavity of AIDS patients and male partners of vaginitis patients, that each strain has a number of general phenotypes, regulated by a reversible, high frequency switching mechanism, which may be utilized under different environmental conditions, and that stains can rapidly evolve at the genetic level. We, therefore, will test the genetic relationship between commensal and infecting strains of the oral cavity of the same individual in the transition from a healthy state to denture stomatitis. For this study, we have developed a computer-assisted DNA fingerprinting system employing the moderately repetitive probe Ca3, and conditions for analyzing phenotype switching. In addition, we will compare commensal and infecting strains from the same individuals for a number of putative virulence traits. This study will answer at the generic level 1) whether phenotypic switching is involved in the transmission from commensalism to pathogenesis, and 4) whether commensal and infecting strains differ in phenotype.